Often this is the result of a problem with the installation. You don't mention whether you are using the Classic CC or the CC version of Lightroom but the procedure is the same.

Please follow these steps:

1. Uninstall Lightroom Classic CC from your Windows machine using the Creative Cloud App.2. Restart your computer. 3. Open the Creative Cloud App and install via the App and it will use a fresh download.

After the reinstallation, do you still see the same same slow behavior?

Can you describe specifically what is slow? Is it importing? Scrolling a grid of thumbnails? Applying a spot brush? Something else. A specific example of behavior that is slow and an idea of how many seconds/minutes it takes will go a long way toward helping us diagnose your slowness. It will also allow us to test the operation and provide you with some comparison for what is expected.